Due to the use of terminals such as smart phones, the average amount mobile communication users increases exponentially and for this, the users' demand for a higher data transmission rate continuously increases.
A method of providing a generally high data transmission rate includes a method of providing communication using a wider frequency band and a method of increasing frequency usage efficiency. Here, the method of increasing the frequency usage efficiency is very difficult to provide a higher average data transmission rate. The reason is because the communication technologies of this generation provide a frequency usage efficiency near a theoretical limit and thus, a technical improvement for increasing the frequency usage efficiency further is difficult. Thus, to increase a data transmission rate, a method of providing data services through a wider frequency band may be considered. In that event, an available frequency band should be considered. In view of the current frequency distribution policy, a band in which a broad band communication of 1 GHz or more is possible is limited and a practically selectable frequency band is only the millimeter wave band of 30 GHz or more. In such a high frequency band, signal attenuation occurs very severely depending on a distance unlike the 2 GHz band used by conventional cellular systems. Due to such signal attenuation, the service providing coverage of a base station that uses power, which is the same with that of the conventional cellular systems, will be considerably reduced. In order to solve this problem, a beam forming technique is widely used which concentrates transmission/reception power to a narrow space so as to increase the transmission/reception efficiency of an antenna.
However, in a beam forming-based communication system, as a beam width increases, a general beam forming effect is reduced in proportion thereto. Also, as the beam width decreases, the beam forming effect further increases. Thus, when one beam width is reduced in order to increase the beam forming effect, the number of transmission beams required for the corresponding base station region increases. Consequently, an overhead for signal transmission increases. That is, since the beam forming effect and the transmission overhead have a trade-off relationship, a measure to increase the beam forming effect while reducing the transmission overhead is desirable.